wah very long nv post lol.. gona post a long wan then hehe
imho.. if you're still getting use to your current power better take your time, don't jump into crazy power though i know its very tempting hehe..
i drive an e9 too.. not mr thou. The stock turbo is very capable and u will see a quite a jump in power with just a tune and increase of boost.
How much u can boost depends on your choice of fuel,list of mods and most importantly tuner. Get a reliable one, then sit down and have a chat with him about your goals. Mine was at 1.6bar (hi).
Know what your car will be use for(daily workhorse,weekend warrior, track whore, etc) and where u want to eventually take it as in power wise..
Go out to more TT and chit chat with the evo's sifus here. Drive your car more often as in really 'drive' but be safe. Know your car limit and your ownself too. That will give you a rough idea.. it will really safe u a lot of problem and $$$ in the future.
Its a never ending story when it comes to cars and modding it.. but a little planning will do wonders.. alot of informative forums out there, do a lil reading and you be suprised what you can learn about your car but take everything with a pinch of salt.
With power also comes with the ability to stop.. don't shortchange your braking mods for power mods :)
cheers and happy boosting~!